1. Scattering Media
A wide range of imaging domains exists in scattering media. Several studies [P. C. Y. Chang, J. C. Flitton, K. I. Hopcraft, E. Jakeman, D. L. Jordan, and J. G. Walker. Improving visibility depth in passive underwater imaging by use of polarization. App. Opt., 42:2794-2803, 2003.; E. Namer and Y. Y. Schechner. Advanced visibility improvement based on polarization filtered images. In Proc. SPIE 5888: Polarization Science and Remote Sensing II, pages 36-45, 2005.; Y. Y. Schechner and N. Karpel. Clear underwater vision. In Proc. IEEE CVPR, volume 1, pages 536-543, 2004.; Y. Y. Schechner, S. G. Narasimhan, and S. K. Nayar. Polarization-based vision through haze. App. Opt., 42:511-525, 2003.; S. Shwartz, E. Namer, and Y. Y. Schechner. Blind haze separation. In Proc. IEEE CVPR, 2006] improved visibility in such media under natural illumination. However, natural light is in general unavailable in relevant scenarios, as in deep water, pipelines, night and biological tissues. Moreover, natural illumination may change in time unpredictably [Y. Y. Schechner and N. Karpel. Attenuating natural flicker patterns. In Proc. MTS/IEEE OCEANS, pages 1262-1268, 2004]. The need to use artificial illumination is therefore obvious. This involves a practical difficulty: the illumination is strongly scattered back towards the camera from particles along the line of sight (LOS), creating backscatter, as shown in FIG. 1. The backscatter overwhelms the signal, causing severe loss of visibility. This problem can be alleviated by increasing the baseline between the light source and the camera [J. S. Jaffe. Computer modelling and the design of optimal underwater imaging systems. IEEE J. Oceanic Eng., 15:101-111, 1990.; B. Skerry and H. Hall. Successful Underwater Photography. New York: Amphoto books, 2002]. However, this is impossible to do in tight environments such as shipwrecks or pipelines. Moreover, a construction using long strobe arms is cumbersome and less hydrodynamic. In any case, backscatter ultimately overcomes the attenuated signal for far enough objects, no matter how far the light source is placed. Backscatter can be modulated and then compensated for in image post-processing. Such current methods require acquisition of long image sequences by structured light [D. M. Kocak and F. M. Caimi. The current art of underwater imaging with a glimpse of the past. MTS Journal, 39:5-26, 2005; M. Levoy, B. Chen, V. Vaish, M. Horowitz, I. McDowall, and M. Bolas. Synthetic aperture confocal imaging. ACM TOG, 23:825-834, 2004; S. G. Narasimhan, S. K. Nayar, B. Sun, and S. J. Koppal. Structured light in scattering media. In Proc. IEEE ICCV, volume 1, pages 420-427, 2005] or time-gating [S. G. Demos and R. R. Alfano. Temporal gating in highly scattering media by the degree of optical polarization. Opt. Letters, 21:161-163, 1996; G. R. Fournier, D. Bonnier, L. J. Forand, and P. W. Pace. Range-gated underwater laser imaging system. Opt. Eng, 32:2185-2190, 1993; Harsdorf, R. Reuter, and S. Tonebon. Contrast-enhanced optical imaging of submersible targets. In Proc. SPIE, volume 3821, pages 378-383, 1999; M. P. Strand. Imaging model for underwater range-gated imaging systems. In Proc. SPIE, volume 1537, pages 151-160, 1991; B. A. Swartz and J. D. Cummings. Laser range-gated underwater imaging including polarization discrimination. In Proc. SPIE., volume 1537, pages 42-56, 1991]. Such sequences may lengthen the overall acquisition time. Moreover, such systems have the drawback of being very complex and expensive.